Single-branch reference for high-frequency phase tracking in 5G and 6G

ABSTRACT

A method is disclosed for mitigating phase noise at high frequencies in 5G and 6G. Quadrature modulation schemes, in which orthogonal branches are amplitude modulated, are susceptible to phase noise which rotates the branches, causing demodulation faults. Disclosed is a single-branch reference signal that can mitigate phase noise. The transmitter can transmit a particular resource element having a normal amplitude in one branch, and zero amplitude in the orthogonal branch. The receiver can then measure the amplitudes of the particular resource element as-received (with phase noise), and determine a phase rotation angle according to a ratio of the two branch amplitudes. The receiver can then correct the branch amplitudes of each message element, and thereby negate the effect of the phase noise. The disclosed procedures can thereby make high-frequency, high-reliability communication feasible, at extremely low cost.

PRIORITY CLAIMS AND RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 63/403,924, entitled “Phase-Noise Mitigation atHigh Frequencies in 5G and 6G”, filed Sep. 6, 2022, and U.S. ProvisionalPatent Application Ser. No. 63/409,888, entitled “Single-BranchReference for High-Frequency Phase Tracking in 5G and 6G”, filed Sep.26, 2022, all of which are hereby incorporated by reference in theirentireties.

FIELD OF THE INVENTION

The disclosure pertains to phase-noise mitigation in wireless messaging,and particularly to phase-noise mitigation at high frequencies.

BACKGROUND OF THE INVENTION

Wireless communication at very high frequencies, such as tens tohundreds of GHz, is needed for the massively increased demand inbandwidth and throughput expected in 5G and 6G. However, phase noise isan increasing problem at higher frequencies, preventing full usage ofthe bandwidth for messaging. What is needed is means for mitigating thephase noise so that the promise of high-speed messaging at highfrequencies can be at least partially realized.

This Background is provided to introduce a brief context for the Summaryand Detailed Description that follow. This Background is not intended tobe an aid in determining the scope of the claimed subject matter nor beviewed as limiting the claimed subject matter to implementations thatsolve any or all of the disadvantages or problems presented above.

SUMMARY OF THE INVENTION

In a first aspect, there is a method for a wireless receiver todemodulate a message, the method comprising: receiving a single-branchreference signal comprising a resource element modulated according to areference I-branch signal multiplexed with an orthogonal referenceQ-branch signal; measuring a reference I-branch amplitude of thereference I-branch signal and a reference Q-branch amplitude of thereference Q-branch signal; calculating a phase rotation angle accordingto a ratio of the reference I-branch amplitude and the referenceQ-branch amplitude; receiving a message comprising message elements,each message element modulated according to an I-branch signal having anI-branch amplitude, multiplexed with an orthogonal Q-branch signalhaving a Q-branch amplitude; adjusting the I-branch amplitude and theQ-branch amplitude according to the phase rotation angle; comparing theadjusted I-branch amplitude to a plurality of predetermined amplitudelevels, and selecting which of the predetermined amplitude levels isclosest to the adjusted I-branch amplitude; and comparing the adjustedQ-branch amplitude to the plurality of predetermined amplitude levels,and selecting which of the predetermined amplitude levels is closest tothe adjusted Q-branch amplitude.

In another aspect, there is a wireless transmitter configured to: use amodulation scheme comprising: a first branch multiplexed with anorthogonal second branch; and a plurality of predetermined amplitudelevels; transmit a single-branch reference signal comprising a referencefirst branch multiplexed with an orthogonal reference second branch,wherein: the reference first branch is amplitude modulated according toone of the predetermined amplitude levels; and the reference secondbranch amplitude modulated with zero amplitude.

In another aspect, there is non-transitory computer-readable media in awireless receiver, the media containing instructions that whenimplemented in a computing environment cause a method to be performed,the method comprising: receiving a single-branch reference signalcomprising, in exactly one resource element, a reference I-branchamplitude multiplexed with an orthogonal reference Q-branch amplitude;measuring the reference I-branch amplitude and the reference Q-branchamplitude; calculating a reference sum-signal amplitude comprising asquare root of a sum of the reference I-branch amplitude squared plusthe reference Q-branch amplitude squared; calculating a referencesum-signal phase comprising an arctangent of a ratio of the referenceQ-branch amplitude divided by the reference I-branch amplitude;receiving a message comprising modulated message elements; for eachmessage element: measuring a received I-branch amplitude and a receivedQ-branch amplitude; calculating a received sum-signal phase according toan arctangent of a ratio of the received Q-branch amplitude divided bythe received I-branch amplitude; and calculating an adjusted sum-signalphase by subtracting the reference sum-signal phase from the receivedsum-signal phase.

This Summary is provided to introduce a selection of concepts in asimplified form. The concepts are further described in the DetailedDescription section. Elements or steps other than those described inthis Summary are possible, and no element or step is necessarilyrequired. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended foruse as an aid in determining the scope of the claimed subject matter.The claimed subject matter is not limited to implementations that solveany or all disadvantages noted in any part of this disclosure.

These and other embodiments are described in further detail withreference to the figures and accompanying detailed description asprovided below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic showing an exemplary embodiment of a 16QAMconstellation chart, according to prior art.

FIG. 1B is a schematic showing an exemplary embodiment of the effect ofphase noise on a 16QAM constellation chart, according to prior art.

FIG. 2A is a schematic showing an exemplary embodiment of asingle-branch reference signal as transmitted, according to someembodiments.

FIG. 2B is a schematic showing an exemplary embodiment of asingle-branch reference signal as received, according to someembodiments.

FIG. 3 is a schematic showing an exemplary embodiment of a resource gridincluding messages, according to some embodiments.

FIG. 4 is a flowchart showing an exemplary embodiment of a procedure formitigating phase noise in a message, according to some embodiments.

FIG. 5 is a sequence chart showing an exemplary embodiment of aprocedure for transmitting and receiving a message with phase-noisemitigation, according to some embodiments.

Like reference numerals refer to like elements throughout.

DETAILED DESCRIPTION

Systems and methods disclosed herein (the “systems” and “methods”, alsooccasionally termed “embodiments” or “arrangements” or “versions” or“examples”, generally according to present principles) can provideurgently needed wireless communication protocols for mitigating theeffects of phase noise at high frequencies planned for late 5G and 6Gcommunications. Disclosed herein is a “single-branch reference signal”,usually occupying just a single resource element, transmitted withorthogonal I and Q branches, in which the I branch is amplitudemodulated according to the one of the predetermined amplitude levels ofthe modulation scheme, while the Q branch is transmitted with zeropower, that is, an amplitude of zero (among other versions). Such asingle-branch reference signal may provide both phase tracking andamplitude calibration, according to the sum-signal phase and thesum-signal amplitude of the single-branch reference signal. For example,a receiver can quantitatively determine the effects of phase noise bydetermining a rotation angle according to a ratio of the as-received Qand I branches. Phase noise generally rotates, or intermingles, the Iand Q branches, resulting in a non-zero amplitude in the reference Qbranch as-received, even if it is transmitted with zero amplitude. Thereceiver can calculate the phase rotation angle according to a ratio ofthe received branch amplitudes. The receiver can then negate phase noisein a message by subtracting that angle from each of the messageelements. More specifically, the receiver can negate phase noise in eachmessage element by calculating a sum-signal phase angle of the messageelement, subtracting the phase angle of the single-branch referencesignal from it, calculating the corrected I and Q amplitudes using thatcorrected phase angle, and then demodulating the message elementaccording to the corrected branch amplitudes, with the phase noisesubstantially negated.

The method is resource-efficient. Using only one branch of one resourceelement, the receiver can negate the phase noise in a large number ofmessage elements encoded in an entire OFDM symbol spanning multiplesubcarriers and, usually, one or two adjacent OFDM symbols as well. Inaddition, the receiver can update the amplitude calibration from theother branch, which is generally modulated according to the maximumbranch amplitude of the modulation scheme (or the same times √2). Thesingle-branch reference signals disclosed herein can negate bothamplitude and phase noise, thereby enabling high frequencycommunications with high reliability, for minimal overhead cost,according to some embodiments.

In one embodiment, the single-branch reference signal is transmittedwith the reference I-branch amplitude equal to the maximum branchamplitude level of the modulation scheme, and the reference Q branchwith zero amplitude. The sum-signal phase is initially zero degrees inthat case, since the reference Q branch is transmitted with zeroamplitude. In another embodiment, the reference Q-branch may have themaximum branch amplitude and the reference I-branch may have zeroamplitude, such that the initial sum-signal phase is 90 degrees. Uponreceiving the single-branch reference signal, the receiver can determinethe phase rotation angle by first calculating a reference phase angleequal to the arctangent of a ratio of the branch amplitudes, and thensubtracting that angle from a predetermined initial reference phaseangle. The difference is the phase rotation angle. For example, when theQ-branch is transmitted with zero amplitude, the initial reference phaseangle is zero, in which case the phase rotation angle is equal to thereceived phase angle. If the single-branch reference signal isconfigured with the I-branch zero, or some other arrangement of branchamplitudes, then the receiver is expected to know how it is configuredso the receiver can calculate the phase rotation angle accordingly.

In some embodiments, one of the branches may have a predeterminedamplitude while the other branch has zero amplitude. The predeterminedamplitude may be the maximum branch amplitude of the modulation scheme,or the maximum sum-signal amplitude of the modulation scheme (which is√2 times the maximum branch amplitude), or other predetermined value.The receiver is expected to know the initial branch amplitude of thesingle-branch reference signal.

In another embodiment, both branches may have the maximum branchamplitude, in which case the sum-signal phase is 45 degrees. It isimmaterial which branch of the single-branch reference signal isselected for zero amplitude, or whether both branches are powered, orother branch-amplitude ratio, so long as the receiver knows the initialsum-signal amplitude and the initial sum-signal phase of the referencesignal, and can thereby determine the effects of noise from the receivedsum-signal amplitude and sum-signal phase. It is generally convenient totransmit one branch with zero amplitude, because the receiver can thenmeasure the rotation angle to high precision according to the receivedamplitude in the orthogonal component. For best SNR, a large amplitudemay be transmitted in the non-zero branch, such as the maximum branchamplitude or the maximum sum-signal amplitude of the modulation scheme,according to some embodiments.

In some embodiments, the single-branch reference signal can be madeoptional, while in other embodiments, the single-branch referencesignals may be automatic or defaulted or compulsory. In someembodiments, a convention or format may be specified in a systeminformation file, such as an SSB (synchronization signal block) or anSIB 1 (system information block number 1) message. The format of thesingle-branch reference signal may include the initial phase angle ofthe reference signal (usually zero degrees if the Q-branch amplitude iszero), the initial amplitude level (usually the maximum branchamplitude, or the maximum sum-signal amplitude, of the modulationscheme), among other variables and parameters. “Initial” in this contextimplies “prior to phase noise distortions”.

In some embodiments, the use and format of single-branch referencesignals may be uniform and automatic, while in other embodiments, eachuser may request a custom format, or select a default conventionindividually. In some embodiments, a system-level convention may specifythe use or format of single-branch reference signals, such as specifyinga particular configuration under certain conditions, or usage when thefrequency is above a certain level. In other embodiments, the use orformat of single-branch reference signals may be assigned by the basestation, and may optionally be configured in an RAR (radio resourcecontrol) message or a Msg4 (fourth message of the 4-step initial accessprocedure) or MsgB (second message of the 2-step initial accessprocedure), or other unicast downlink message. In some embodiments, theuse or format of the single-branch reference signals may be requested bya user device in an uplink message such as a Msg3 (third message of the4-step initial access procedure) or MsgA (first message of the 2-stepinitial access procedure) or other message.

In some embodiments, a single-branch reference signal may be required atthe head (initial subcarrier or symbol-time) of a message by default.The leading single-branch reference signal may thereby compensate phasenoise in message elements which are (temporally) proximate to thesingle-branch reference signal. In some embodiments, a base station mayprovide single-branch reference signals periodically during intervalsscheduled for downlink, and optionally in unscheduled intervals as well.For example, the base station can transmit one of the single-branchreference signals in each symbol-time, or one per two symbol-times, orother interval as specified in system information files or conventions.In some embodiments, the use of single-branch reference signals may bedifferent for uplink and downlink messages, such as being provided bythe base station in downlink but not by the user device in uplink, orvice-versa. In some embodiments, the use of single-branch referencesignals for phase tracking and phase-noise mitigation may depend on thefrequency, for example requiring single-branch reference signals at highfrequencies, not requiring them at low frequencies, and making themoptional at intermediate frequencies. In some embodiments, the use ofsingle-branch reference signals may be based on the rate of phase faultsin messages. For example, the receiver can require the use ofsingle-branch reference signals when the rate of phase faults is high,and can decline them when phase faults are below a threshold. In someembodiments, the single-branch reference signals by be provided to eachuser only if needed. For example, a simple user device with a low-costsemiconductor clock may have more need for phase-noise mitigation than ahigh-performance user with an atomically stabilized time-base. In someembodiments, each user device that detects phase faults above a certainrate may request the phase-noise mitigation service when needed toachieve a required QoS level, or for message reliability at highfrequencies, or to avoid retransmission requests, or to conserveresources, or for other reason.

Since the single-branch reference signals generally occupy only oneresource element, and involve transmitted power in only one branch, theyimpose a negligible resource cost and power overhead, yet provide bothphase-noise mitigation and amplitude calibration transparently.

The examples presented below are suitable for adoption by a wirelessstandards organization. Standardizing the single-branch referencesignals may thereby provide the benefits of automatic and transparentphase-noise mitigation at negligible cost in power and resources, andmay thereby benefit billions of future wireless users worldwide, in 5Gand 6G and beyond.

Terms herein generally follow 3GPP (third generation partnershipproject) standards, but with clarification where needed to resolveambiguities. As used herein, “5G” represents fifth-generation, and “6G”sixth-generation, wireless technology in which a network (or cell or LANLocal Area Network or RAN Radio Access Network or the like) may includea base station (or gNB or generation-node-B or eNB or evolution-node-Bor AP Access Point) in signal communication with a plurality of userdevices (or UE or User Equipment or user nodes or terminals or wirelesstransmit-receive units) and operationally connected to a core network(CN) which handles non-radio tasks, such as administration, and isusually connected to a larger network such as the Internet. Thetime-frequency space is generally configured as a “resource grid”including a number of “resource elements”, each resource element being aspecific unit of time termed a “symbol period” or “symbol-time”, and aspecific frequency and bandwidth termed a “subcarrier” (or “subchannel”in some references). Symbol periods may be termed “OFDM symbols”(Orthogonal Frequency-Division Multiplexing) in references. The timedomain may be divided into ten-millisecond frames, one-millisecondsubframes, and some number of slots, each slot including 14 symbolperiods. The number of slots per subframe ranges from 1 to 8 dependingon the “numerology” selected. The frequency axis is divided into“resource blocks” (also termed “resource element groups” or “REG” or“channels” in references) including 12 subcarriers, each subcarrier at aslightly different frequency. The “numerology” of a resource gridcorresponds to the subcarrier spacing in the frequency domain.Subcarrier spacings of 15, 30, 60, 120, and 240 kHz are defined invarious numerologies. Each subcarrier can be independently modulated toconvey message information. Thus a resource element, spanning a singlesymbol period in time and a single subcarrier in frequency, is thesmallest unit of a message. “Classical” amplitude-phase modulationrefers to message elements modulated in both amplitude and phase,whereas “quadrature” or “PAM” (pulse-amplitude) modulation refers to twosignals, separately amplitude-modulated, and then multiplexed andtransmitted with a 90-degree phase shift between them. The twomultiplexed signals may be called the “I” and “Q” branch signals (forIn-phase and Quadrature-phase) or “real and imaginary” among others.Standard modulation schemes in 5G and 6G include BPSK (binaryphase-shift keying), QPSK (quad phase-shift keying), 16QAM (quadratureamplitude modulation with 16 modulation states), 64QAM, 256QAM andhigher orders. Most of the examples below relate to QPSK or 16QAM, withstraightforward extension to the other levels of modulation. QPSK isphase modulated but not amplitude modulated. 16QAM may be modulatedaccording to PAM which exhibits two phase levels at zero and 90 degrees(or in practice, for carrier suppression, ±45 degrees) and fouramplitude levels including two positive and two negative amplitudelevels, thus forming 16 distinct modulation states. For comparison,classical amplitude-phase modulation in 16QAM includes four positiveamplitude levels and four phases of the raw signal, which aremultiplexed to produce the 16 states of the modulation scheme. “SNR”(signal-to-noise ratio) and “SINK” (signal-to-interference-and-noiseratio) are used interchangeably unless specifically indicated. “RRC”(radio resource control) is a control-type message from a base stationto a user device. “Digitization” refers to repeatedly measuring awaveform using, for example, a fast ADC (analog-to-digital converter) orthe like. An “RF mixer” is a device for multiplying an incoming signalwith a local oscillator signal, thereby selecting one component of theincoming signal.

In addition to the 3GPP terms, the following terms are defined herein.Although in references a modulated resource element of a message may bereferred to as a “symbol”, this may be confused with the same term for atime interval (“symbol-time”), among other things. Therefore, eachmodulated resource element of a message is referred to as a “modulatedmessage resource element”, or more simply as a “message element”, inexamples below. A “demodulation reference” is a set of Nref modulated“reference resource elements” or “reference elements” modulatedaccording to the modulation scheme of the message and configured toexhibit levels of the modulation scheme (as opposed to conveying data).Thus integer Nref is the number of reference resource elements in thedemodulation reference. A “calibration set” is one or more amplitudevalues (and optionally phase values), which have been determinedaccording to a demodulation reference, representing the predeterminedmodulation levels of a modulation scheme. A “short-form” demodulationreference is a demodulation reference that exhibits the maximum andminimum amplitude levels of the modulation scheme, from which thereceiver can determine any intermediate levels by interpolation. “RF” orradio-frequency refers to electromagnetic waves in the MHz (megahertz)or GHz (gigahertz) frequency ranges. The “raw” signal is the as-receivedwaveform before separation of the quadrature branch signals. “Phasenoise” is random noise or time jitter that alters the phase of areceived signal, usually without significantly affecting the overallamplitude. “Phase-noise tolerance” is a measure of how much phasealteration can be imposed on an allowed state without causing ademodulation fault. A “faulted” message has at least one incorrectlydemodulated message element. A “phase fault” is a message elementdemodulated as a state differing in phase from the intended modulationstate, whereas an “amplitude fault” is a message element demodulated asa state differing in amplitude from the intended modulation state.

Referring to quadrature or PAM modulation, an “I-Q” space is an abstracttwo-dimensional space defined by an I-branch amplitude and an orthogonalQ-branch amplitude, in which each transmitted message element occupiesone of several predetermined I-Q states of a modulation scheme. When theorthogonal branches are called “real” and “imaginary”, the I-Q space issometimes called the “complex plane”.

The receiver may process the received signals by determining a“sum-signal”, which is the vector sum of the I and Q branch signals. Avector sum is a sum of two vectors, in this case representing theamplitudes and phases of the two orthogonal branches in I-Q space. Thesum-signal has a “sum-signal amplitude”, equal to the square root of thesum of the I and Q branch amplitudes squared (the “root-sum-square” of Iand Q), and a “sum-signal phase”, equal to the arctangent of the ratioof the I and Q signal amplitudes (plus an optional base phase, which isignored herein). When a message element is received at a receiver, thereceived I and Q amplitudes may be substantially different from thetransmitted values due to phase noise, which generally intermingles thetwo branches. Phase noise tends to change the ratio of I and Qamplitudes, but does not tend to change the overall amplitude of themessage element (absent amplifier nonlinearities, which are ignoredherein). Therefore, the receiver can correctly demodulate the message bydetermining a phase rotation angle according to a single-branchreference signal, and then de-rotating the sum-signal phase of eachmessage element to negate phase noise.

Turning now to the figures, a prior-art modulation scheme is susceptibleto phase noise at high frequencies.

FIG. 1A is a schematic showing an exemplary embodiment of a 16QAMconstellation chart, according to prior art. As depicted in thisprior-art example, a modulation scheme 101 includes 16 allowedmodulation states 102, each allowed state determined by an I-branchsignal and a Q-branch signal orthogonal to the I-branch signal (forexample, the Q-branch phase-modulated at 90 degrees relative to theI-branch). The horizontal axis shows the amplitude modulation of theI-branch signal, and the vertical axis shows the amplitude modulation ofthe Q-branch signal, each branch being amplitude-modulated at one ofcertain predetermined amplitude levels of the modulation scheme. In thiscase, the predetermined amplitude levels are −3, −1, +1, and +3arbitrary units. The various amplitude levels are equally separated andsymmetrical around zero. The central cross-shape represents zeroamplitude. Negative amplitude levels are equivalent to a 180-degreephase change. There are 16 states, as expected for 16QAM. A receiver canreceive a message element modulated according to this modulation scheme,and can extract the I and Q branches separately by analog or digitalsignal-processing means. The receiver can then measure the amplitudes ofthose two branches, compare the measured amplitude values to apredetermined set of amplitude levels, select the closest match to eachbranch amplitude, and thereby determine the modulation state of themessage element. 16QAM encodes 4 bits per message element.

FIG. 1B is a schematic showing an exemplary embodiment of the effect ofphase noise on a 16QAM constellation chart, according to prior art. Asdepicted in this prior-art example, the modulation states 112 of a 16QAMconstellation chart 111 can be distorted (“smeared out”) by phase noisein a characteristic way as indicated by phase distortion clouds 118. Thedepicted distortions would be caused by moderate phase noise at moderatefrequencies; at high frequencies it is much worse. If the samemodulation scheme were attempted at the much higher frequencies plannedfor future wireless operation, the phase noise would be much larger thandepicted, and the phase-noise clouds would substantially overlap,resulting in frequent message faults. Hence the need for strategies toenable communication despite strong phase distortions.

FIG. 2A is a schematic showing an exemplary embodiment of asingle-branch reference signal as transmitted, according to someembodiments. As depicted in this non-limiting example, a constellationchart 201 for 16QAM is shown with various modulation states as circles203 indicating the I and Q branch amplitudes of each state 203. Alsoshown is a single dot indicating a single-branch reference signal 202,as transmitted by a transmitter, without phase noise. In this case, theI-branch of the single-branch reference signal 202 is amplitudemodulated according to the maximum branch amplitude level 204 of themodulation scheme, while the Q-branch has zero amplitude. Thus thesingle-branch reference signal 202 has an initial sum-signal amplitude204 equal to the maximum branch amplitude of the modulation scheme, andan initial sum-signal phase of zero degrees. The single-branch referencesignal 202 is distinct from all of the 16QAM allowed states 203, sincethe allowed states generally do not have a zero-amplitude branch, do nothave a sum-signal amplitude equal to one of the branch amplitude levelsof the modulation scheme, and do not have a sum-signal phase of zerodegrees.

In other embodiments, the single-branch reference signal may betransmitted with zero amplitude in the I-branch and a non-zero amplitudein the Q-branch instead of the depicted version. Alternatively, thesingle-branch reference signal may be transmitted with equal amplitudesin both branches with 45 degree initial phase, or some other phase upontransmission, so long as the receiver knows the initial amplitude andphase. The receiver, upon measuring the I and Q branches as-received,can calculate the phase rotation angle due to phase noise according tothe received I and Q branch amplitudes. The receiver can then receive amessage and correct each message element by de-rotating by the phaserotation angle, and then demodulate according to the corrected branchamplitudes of the message element.

In some embodiments, the receiver may determine the sum-signal amplitudeand sum-signal phase of a single-branch reference signal, by measuringproperties of the as-received waveform directly, instead of separatingthe I and Q branches. For example, the receiver can calculate a phaserotation angle by comparing the received phase to the transmitted phaseof the single-branch reference signal. The receiver can then subtractthe phase rotation angle from each of the message elements, thenseparate the corrected I and Q branches of the message elements, andthereby demodulate the message with phase noise negated.

FIG. 2B is a schematic showing an exemplary embodiment of asingle-branch reference signal as received, according to someembodiments. As depicted in this non-limiting example, a constellationchart 211, such as that of the previous figure, includes 16QAMmodulation states 213. Also shown is a single-branch reference signal212 as-received, including phase noise that rotates the phase through aphase rotation angle 217 relative to the initial phase, which is zerodegrees since Q is initially zero amplitude. The as-received I-branchamplitude 214 is smaller than the transmitted I-branch amplitude 204 dueto the rotation, and the Q-branch amplitude 215 has been increased dueto the rotation. For comparison, the initial transmitted modulation isshown as an “X” 216. The phase noise causes a phase rotation by thephase rotation angle 217, but the sum-signal amplitude 218 as-receivedis the same as the sum-signal amplitude 204 as-transmitted.

The receiver can measure the amplitudes of the as-received I and Qbranches, calculate the phase rotation angle (as the arctan(Q/I)), andthen use that angle to negate the phase noise in message elements. Eachsingle-branch reference signal can correct the phase in message elementstransmitted in the same symbol-time, and optionally in adjacent or otherclosely proximate symbol-times, depending on the frequency spectrum ofthe phase noise. In a first embodiment, the receiver can determine thephase rotation angle, then receive and process the message elements byseparating their I and Q branch signals, measuring the I and Q branchamplitudes of each message element, correcting the message branchamplitudes according to the phase rotation angle, and then demodulatingthe message by comparing the corrected branch amplitudes to thepredetermined amplitude levels of the modulation scheme. For example,the receiver can calculate the sum-signal amplitude and sum-signal phaseof each message element from the received I and Q branch amplitudes,then subtract the phase rotation angle from the sum-signal phase, andthen calculate the corrected I and Q amplitudes according to thecorrected sum-signal phase. The sum-signal amplitude is generallyunchanged by phase noise.

In a second embodiment, the receiver can determine the phase rotationangle as described, and can then adjust the local time-base offset orphase zero to negate the phase rotation angle. Alternatively, andequivalently, the receiver can adjust a time offset equal to the phaserotation angle divided by 2πf, where f is the frequency. In either case,the receiver can then separate the I and Q branches using that adjustedtime-base, with the phase noise negated.

In a third embodiment, the receiver can determine the phase rotationangle, and then adjust the branch-separation phases of the I and Qbranches before processing the message elements. (The branch-separationphase is the phase at which the receiver determines the I and Q branchamplitudes.) The branch-separation phase is normally zero for theI-branch and 90 degrees for the Q-branch (or ±45 degrees if carriersuppression is enforced). To negate phase noise, the receiver caninstead use a branch-separation phase of −θ for the I-branch, and 90-θfor the Q-branch (with θ representing the phase rotation angle). Thereceiver can then separate and processes the two branches at thoserevised phases, with phase noise largely negated.

After determining the de-rotated I and Q branch amplitudes by any ofthese methods, or other signal processing methods that artisans maydevise after reading this disclosure, the receiver can then demodulatethe message element by comparing the corrected I and Q amplitudes to thepredetermined amplitude levels of the modulation scheme, with theeffects of phase noise largely removed.

FIG. 3 is a schematic showing an exemplary embodiment of a resource gridincluding messages, according to some embodiments. As depicted in thisnon-limiting example, a resource grid 301 is defined by symbol-times 302and subcarriers 303. A first message “M” 304 is frequency-spanning(occupying multiple subcarriers at a single symbol-time) and is headedby a single-branch reference signal 305 configured to provide phase andamplitude modulation information for demodulating the rest of themessage 304. In this case, the single-branch reference signal 305 is asingle resource element originally transmitted with an I-branchamplitude according to the maximum branch amplitude level of themodulation scheme, and a Q-branch transmitted with zero amplitude. Thereceiver can measure the as-received I and Q signals, measure theiramplitudes, and calculate the sum-signal phase according to a ratio ofthe Q and I amplitudes. The sum-signal phase is non-zero in this case,due to phase noise. Since the initial phase was zero, the receivedsum-signal phase equals the phase rotation angle. The receiver can alsocalculate the sum-signal amplitude as the root-sum-square (square rootof the sum of the squares) of the as-received I and Q amplitudes. Thereceiver can use the sum-signal amplitude of the single-branch referencesignal to update the predetermined amplitude levels of the modulationscheme, and thereby mitigate amplitude noise. For example, the receivercan determine a “correction ratio”, which is equal to the sum-signalamplitude of the single-branch reference signal divided by the initialamplitude of the I-branch. Normally the powered branch of thesingle-branch reference signal is set to the largest branch amplitude ofthe modulation scheme or the largest sum-signal amplitude (or otherknown amplitude of the modulation scheme). The receiver can thenmultiply all of the predetermined amplitude levels of the modulationscheme by the correction ratio, and thereby mitigate the currentamplitude noise.

The receiver can mitigate phase noise by subtracting the phase rotationangle from each of the message elements, and can mitigate amplitudenoise by adjusting the predetermined amplitude levels of the modulationscheme according to the calculated sum-signal amplitude of thesingle-branch reference signal. The figure shows the single-branchreference signal 305 in the same symbol-time as the message 304.However, in many cases, the message may be in an adjacent symbol-time tothe reference signal, or spaced apart from the reference signal by twoor three or more symbol-times, depending on how rapidly the phase noisechanges over time. In general, the receiver can mitigate both amplitudenoise and phase noise in multiple messages at multiple symbol-times,using the amplitude and phase information provided in the single-branchreference signal 305, with an overhead burden of just one resourceelement.

Also shown is a time-spanning message 307, that is, a message occupyingmultiple symbol-times at a single subcarrier. The message 307 includes asingle-branch reference signal 308 in which the I-branch equals themaximum branch amplitude of the modulations scheme and the Q-branch haszero amplitude. As mentioned, the receiver can recalibrate thepredetermined amplitude levels of the modulation scheme by determiningthe sum-signal amplitude of the reference 308, and can negate phasenoise by calculating a sum-signal phase of the reference 308as-received. The message includes message elements “M” in which both Iand Q branches are amplitude-modulated according to the message content,and at least one single-branch reference signal “I/Z” 309 in which the Ibranch is amplitude-modulated according to the message content, but theQ-branch is modulated as zero amplitude, upon transmission. Thus the“I/Z” reference 309 can provide phase noise mitigation according to theQ-branch, and can also provide further message content which is encodedin the non-zero branch (such as the I-branch), as-transmitted. Thereceiver can then negate phase noise according to the sum-signal phase,and can demodulate part of the message according to the sum-signalamplitude. For example, if the modulation scheme has 4 predeterminedamplitude levels (such as 16QAM), the sum-signal amplitude can convey 2bits of message information, while the sum-signal phase can providephase-noise mitigation.

In the depicted case, the message 307 includes one single-branchreference signals for every two message elements. The receiver canupdate the phase rotation angle according to the ratio of received Q andI branches in those references 309, and can demodulate message bitsaccording to the sum-signal amplitude (which is a measure of theoriginally transmitted I-branch amplitude). Thus the depicted message307 provides a phase noise correction periodically at multiplesymbol-times throughout the message 307. In the depicted case, theoverhead burden is one branch for each two message elements, while threebranches carry message data for each two message elements (except forthe first one 308, which instead indicates the maximum amplitude levelfor calibration).

Also shown is a series of phase-tracking single-branch reference signals306 “PT” placed periodically in the resource grid 301 on one subcarrier,which in this case is the first subcarrier, but could be any one of thesubcarriers in the block. For example, the base station can transmitsuch a phase-tracking single-branch reference signal 306 during eachresource grid portion that has been scheduled for downlink, andoptionally for each portion that is unscheduled, to providenear-continuous phase noise updating. Each of the phase-trackingsingle-branch reference signals 306 is transmitted with an I branchmodulated at a standard amplitude, and a Q-branch modulated at zeroamplitude. As-received, the phase-tracking single-branch referencesignals 306 are generally phase-rotated due to phase noise, causing someof the I-branch amplitude to rotate into the Q-branch. The receiver canmeasure the I and Q amplitudes of each of the phase-trackingsingle-branch reference signals 306, and thereby calculate an updatedrotation angle, at multiple symbol-times in the grid. Receivers can thendemodulate their messages elsewhere in the grid, instead of includinguser-specific phase tracking elements in the messages. Hence theindividual messages can use the phase-noise mitigation provided by thephase-tracking single-branch reference signals 306 to correct the phasenoise before demodulating their message elements. For example, a basestation may insert such phase-tracking single-branch reference signalsperiodically in the downlink channels, thereby enabling each user tomitigate phase noise in its received messages.

In some embodiments, the receiver (such as a user device) can prompt thetransmitter (such as a base station) to include single-branch referencesignals for phase-tracking periodically in the resource grid, when thereceiver determines that the rate of phase faults is above a threshold.Likewise, the receiver can include a single-branch reference signal,such as 309, periodically within an uplink message, while continuing toencode message bits in the non-zero branch of each single-branchreference signal within the message, as mentioned.

The phase-tracking single-branch reference signals 306 are shownrepeated every fourth symbol-time in this case. Depending on propertiesof the phase noise (such as the size of the phase rotation angle onaverage, or the time over which the phase rotation angle typicallychanges), the phase-tracking single-branch reference signals 306 may beplaced closer together, such as 2 or 3 symbol-times apart, or fartherapart such as 1 or 2 reference signals per subframe. In extreme phasenoise cases, the phase-tracking single-branch reference signals 306 maybe included in each downlink symbol-time.

The figure shows a variety of configurations for implementing thesingle-branch reference signals for phase-noise mitigation. In someembodiments, mitigation procedures may be standardized and compulsory,such as applying a single-branch reference signal at the start of eachmessage or periodically within time-spanning messages, and on downlink,in certain symbol-times of each subframe for example. In otherembodiments, the single-branch reference signals may be applied onlywhen desired for enhanced message reliability, such as at highfrequencies or when the user device has a noisy clock for example.Options and choices, as well as conventions and formats, may be providedin system information files, such as the synchronization files andinitial access messages that all user devices receive upon registeringwith a base station. Alternatively, if the use of such mitigation is tobe voluntary, a user device may request same upon joining a network.

FIG. 4 is a flowchart showing an exemplary embodiment of a procedure formitigating phase noise in a message, according to some embodiments. Asdepicted in this non-limiting example, at 401 a transmitter and areceiver determine or receive or otherwise learn of a modulation schemethat includes integer Nstates allowed modulation states in an I-Q space,such as 16QAM, and a plurality of predetermined amplitude levels, suchas −3, −1, +1, +3 of 16QAM. At 402, the transmitter modulates a messageaccording to the modulation scheme, and transmits a single-branchreference signal followed (in time or in frequency) by the message. Thesingle-branch reference signal is transmitted with a known sum-signalphase. In this example, the transmitted Q branch amplitude is zero, sothe transmitted sum-signal phase is also zero. The single-branchreference signal is transmitted with a known sum-signal amplitude. Inthis example, the transmitted I branch amplitude equals the maximumbranch amplitude level (+3 units) of the modulation scheme, and the Qamplitude is zero, so the transmitted sum-signal amplitude equals themaximum branch amplitude level.

At 403, the receiver receives the single-branch reference signal andmeasures the received reference I and Q branch amplitudes therein.Generally, due to phase noise, the received reference I and Q branchamplitudes are different from those transmitted. At 404, the receivercalculates a phase rotation angle based on the received reference I andQ branch amplitudes. For example, the receiver can calculate thearctangent of the received reference Q amplitude divided by the receivedreference I amplitude. In this example, the transmitted sum-signal phaseis zero degrees; hence the phase rotation angle is directly equal to thereceived reference sum-signal phase. In other embodiments, thesingle-branch reference signal may be transmitted with a differentsum-signal phase, such as 90 degrees. In each case, the transmittedphase is known to the receiver, so the receiver can readily determinethe phase rotation angle from the received reference sum-signal phase.

At 405, the receiver calculates a received reference sum-signalamplitude (sometimes called a waveform magnitude) from the receivedreference branch amplitudes, such as the root-sum-square of the receivedreference I and Q amplitudes. The receiver then calculates an amplitudeadjustment by comparing the received reference sum-signal amplitude tothe transmitted reference sum-signal amplitude. In this case thetransmitted reference sum-signal amplitude is the transmitted I branchamplitude, which equals the maximum branch amplitude of the modulationscheme, or +3 units for 16QAM. The receiver is expected to know thetransmitted reference sum-signal amplitude and phase, or equivalently,the transmitted I and Q branch amplitudes.

The receiver can then calculate an amplitude adjustment factor as adifference or as a ratio, depending on the implementation. Formitigating additive noise, the amplitude adjustment factor equals thereceived reference sum-signal amplitude minus the transmitted referencesum-signal amplitude, since the received version includes additiveamplitude noise. Hence, the receiver can mitigate additive amplitudenoise by subtracting the amplitude adjustment factor from the messageelements, as discussed below. In other implementations, the amplitudeadjustment factor may be calculated as a ratio of the transmitted andreceived reference sum-signal amplitudes, in which case the receiver canmitigate complex amplitude noise by multiplying or dividing the messageamplitudes by that factor. In this example, additive noise is assumed.

At 406, the receiver receives a message element, separates the receivedmessage I and Q branches, and measures the received message I and Qamplitudes. At 407, the receiver determines a received messagesum-signal phase according to a ratio of the received message Qamplitude divided by the received message I amplitude. The receiver thensubtracts the phase rotation angle from the received message sum-signalphase, thereby determining a corrected message sum-signal phase.

At 408, the receiver determined a received message sum-signal amplitudesuch as the root-sum-square of the received message I and Q amplitudes.The receiver than subtracts the amplitude adjustment factor from themessage sum-signal amplitude, thereby determining a phase-corrected andamplitude-adjusted message sum-signal amplitude and phase. The receiverthen calculates mitigated I and Q amplitudes from the corrected adjustedsum-signal amplitude and phase. For example, the receiver can calculatethe final I branch amplitude as the amplitude-adjusted sum-signalamplitude times the cosine of the phase-corrected sum-signal phase, andthe final Q branch amplitude as the amplitude-adjusted sum-signalamplitude times the sine of the phase-corrected sum-signal phase.

At 409, the receiver demodulates the message element by comparing thephase-corrected, amplitude-adjusted final message I and Q amplitudes tothe predetermined amplitude levels of the modulation scheme, selectingthe closest match in each case.

In an alternative embodiment, the receiver may amplitude-adjust the setof predetermined amplitude levels instead of the message sum-signalamplitude, thereby causing the calibration set to vary and track thevarying noise environment in real-time. In other embodiments, thereceiver can phase-correct the assumed transmitted sum-signal phaseinstead of the message sum-signal phase. It is immaterial whether thephase and amplitude corrections are applied to the transmitted orreceived or predetermined values, so long as it is done consistently.

In summary, the receiver has used its knowledge of the transmittedreference branch amplitudes to calculate a phase rotation angle and anamplitude adjustment factor, and has thereby mitigated both the phasenoise and the amplitude noise in the demodulated the message element.

FIG. 5 is a sequence chart showing an exemplary embodiment of aprocedure for transmitting and receiving a message with phase-noisemitigation, according to some embodiments. As depicted in thisnon-limiting example, actions of a transmitter are shown on the firstline, of a receiver on the second line, and time is horizontal witharrows showing causation. At 501, a transmitter determines a modulationscheme with predetermined amplitude levels and quadrature modulation oforthogonal branch signals. At 502, the transmitter transmits asingle-branch reference signal consisting of one resource element withan I-branch having the maximum branch amplitude level of the modulationscheme, and the Q-branch having zero amplitude. At 503, the transmitterthen transmits the rest of the message elements.

At 504, the receiver receives the single-branch reference signal and at505 determines a sum-signal amplitude and a sum-signal phase accordingto the I and Q branch amplitudes as-received. The receiver recalibratesa set of predetermined branch amplitude levels of the modulation schemeaccording to the sum-signal amplitude of the single-branch referencesignal.

At 506, the receiver receives the message and determines the I and Qamplitudes, including phase noise and amplitude noise, of each messageelement. At 507, the receiver corrects the branch amplitudes of eachmessage element, by de-rotating them opposite to the phase rotationangle, as determined from the single-branch reference signal. At 508,the receiver demodulates the corrected branch amplitudes by comparingthe phase-corrected branch amplitudes to the recalibrated amplitudelevels of the modulation scheme. At 509, the receiver transmits anacknowledgement which the transmitter receives at 510.

Thus the message has been transmitted with both amplitude and phasecorruption, but by using the single-branch reference signal to mitigateeach branch of each message element, the receiver has mitigated both theamplitude and phase noise, and thereby demodulated the message torecover its original content.

The de-rotation of the message element may be performed in a variety ofways, depending on implementation. In one embodiment, the receiver cancalculate the sum-signal amplitude and sum-signal phase of a messageelement, subtract the phase rotation angle from the sum-signal phase toget a corrected sum-signal phase of the message element, and thenreconstruct the branches trigonometrically. More specifically, thereceiver can calculate the corrected I-branch amplitude of the messageelement as the sum-signal amplitude times the cosine of the correctedsum-signal phase, and can calculate the corrected Q-branch amplitude asthe sum-signal amplitude times the sine of the corrected sum-signalphase. Artisans may devise other, equivalent, calculation procedures fordetermining the message element branch amplitudes with the phase noiseremoved.

Due to the many options and variations disclosed herein, and otherversions derived therefrom by artisans after reading this disclosure, itwould be helpful for a wireless standards committee to establishconventions governing the use, incidence, and formats of single-branchreference signals, so that future wireless users can enjoy phase-noisemitigation transparently with each communication.

The wireless embodiments of this disclosure may be aptly suited forcloud backup protection, according to some embodiments. Furthermore, thecloud backup can be provided cyber-security, such as blockchain, to lockor protect data, thereby preventing malevolent actors from makingchanges. The cyber-security may thereby avoid changes that, in someapplications, could result in hazards including lethal hazards, such asin applications related to traffic safety, electric grid management, lawenforcement, or national security.

In some embodiments, non-transitory computer-readable media may includeinstructions that, when executed by a computing environment, cause amethod to be performed, the method according to the principles disclosedherein. In some embodiments, the instructions (such as software orfirmware) may be upgradable or updatable, to provide additionalcapabilities and/or to fix errors and/or to remove securityvulnerabilities, among many other reasons for updating software. In someembodiments, the updates may be provided monthly, quarterly, annually,every 2 or 3 or 4 years, or upon other interval, or at the convenienceof the owner, for example. In some embodiments, the updates (especiallyupdates providing added capabilities) may be provided on a fee basis.The intent of the updates may be to cause the updated software toperform better than previously, and to thereby provide additional usersatisfaction.

The systems and methods may be fully implemented in any number ofcomputing devices. Typically, instructions are laid out on computerreadable media, generally non-transitory, and these instructions aresufficient to allow a processor in the computing device to implement themethod of the invention. The computer readable medium may be a harddrive or solid state storage having instructions that, when run, orsooner, are loaded into random access memory. Inputs to the application,e.g., from the plurality of users or from any one user, may be by anynumber of appropriate computer input devices. For example, users mayemploy vehicular controls, as well as a keyboard, mouse, touchscreen,joystick, trackpad, other pointing device, or any other such computerinput device to input data relevant to the calculations. Data may alsobe input by way of one or more sensors on the robot, an inserted memorychip, hard drive, flash drives, flash memory, optical media, magneticmedia, or any other type of file-storing medium. The outputs may bedelivered to a user by way of signals transmitted to robot steering andthrottle controls, a video graphics card or integrated graphics chipsetcoupled to a display that maybe seen by a user. Given this teaching, anynumber of other tangible outputs will also be understood to becontemplated by the invention. For example, outputs may be stored on amemory chip, hard drive, flash drives, flash memory, optical media,magnetic media, or any other type of output. It should also be notedthat the invention may be implemented on any number of different typesof computing devices, e.g., embedded systems and processors, personalcomputers, laptop computers, notebook computers, net book computers,handheld computers, personal digital assistants, mobile phones, smartphones, tablet computers, and also on devices specifically designed forthese purpose. In one implementation, a user of a smart phone orWi-Fi-connected device downloads a copy of the application to theirdevice from a server using a wireless Internet connection. Anappropriate authentication procedure and secure transaction process mayprovide for payment to be made to the seller. The application maydownload over the mobile connection, or over the Wi-Fi or other wirelessnetwork connection. The application may then be run by the user. Such anetworked system may provide a suitable computing environment for animplementation in which a plurality of users provide separate inputs tothe system and method.

It is to be understood that the foregoing description is not adefinition of the invention but is a description of one or morepreferred exemplary embodiments of the invention. The invention is notlimited to the particular embodiments(s) disclosed herein, but rather isdefined solely by the claims below. Furthermore, the statementscontained in the foregoing description relate to particular embodimentsand are not to be construed as limitations on the scope of the inventionor on the definition of terms used in the claims, except where a term orphrase is expressly defined above. Various other embodiments and variouschanges and modifications to the disclosed embodiment(s) will becomeapparent to those skilled in the art. For example, the specificcombination and order of steps is just one possibility, as the presentmethod may include a combination of steps that has fewer, greater, ordifferent steps than that shown here. All such other embodiments,changes, and modifications are intended to come within the scope of theappended claims.

As used in this specification and claims, the terms “for example”,“e.g.”, “for instance”, “such as”, and “like” and the terms“comprising”, “having”, “including”, and their other verb forms, whenused in conjunction with a listing of one or more components or otheritems, are each to be construed as open-ended, meaning that the listingis not to be considered as excluding other additional components oritems. Other terms are to be construed using their broadest reasonablemeaning unless they are used in a context that requires a differentinterpretation.

The invention claimed is:
 1. A method for a wireless receiver todemodulate a message, the method comprising: a) receiving asingle-branch reference signal comprising a resource element modulatedaccording to a reference I-branch signal multiplexed with an orthogonalreference Q-branch signal; b) measuring a reference I-branch amplitudeof the reference I-branch signal and a reference Q-branch amplitude ofthe reference Q-branch signal; c) calculating a phase rotation angleaccording to a ratio of the reference I-branch amplitude and thereference Q-branch amplitude; d) receiving a message comprising messageelements, each message element modulated according to an I-branch signalhaving an I-branch amplitude, multiplexed with an orthogonal Q-branchsignal having a Q-branch amplitude; e) adjusting the I-branch amplitudeand the Q-branch amplitude according to the phase rotation angle; f)comparing the adjusted I-branch amplitude to a plurality ofpredetermined amplitude levels, and selecting which of the predeterminedamplitude levels is closest to the adjusted I-branch amplitude; and g)comparing the adjusted Q-branch amplitude to the plurality ofpredetermined amplitude levels, and selecting which of the predeterminedamplitude levels is closest to the adjusted Q-branch amplitude.
 2. Themethod of claim 1, wherein the message is received according to 5G or 6Gtechnology.
 3. The method of claim 1, further comprising: a) determininga reference phase angle comprising an arctangent of a ratio of thereference Q-branch amplitude divided by the reference I-branchamplitude; and b) calculating the phase rotation angle by subtractingthe received reference phase angle from a predetermined initialreference phase angle.
 4. The method of claim 3, wherein the initialreference phase angle is zero degrees.
 5. The method of claim 1, furthercomprising: a) determining a reference sum-signal amplitude equal to asquare root of a sum of the reference I-branch amplitude squared plusthe reference Q-branch amplitude squared; b) determining a correctionratio comprising the reference sum-signal amplitude divided by apreviously determined amplitude level; and c) multiplying each of thepredetermined amplitude levels of the plurality by the correction ratio.6. The method of claim 1, further comprising: a) determining, accordingto a system information file, a format of the single-branch referencesignal; b) wherein the format of the single-branch reference signalcomprises an initial reference phase and an initial reference amplitude.7. The method of claim 1, further comprising: a) determining a rate ofphase faults, wherein each phase fault is a message element that isincorrectly demodulated due to phase noise; and b) if the rate of phasefaults exceeds a predetermined threshold, transmitting a messagerequesting that each subsequent transmission to the receiver shouldinclude at least one single-branch reference signal.
 8. The method ofclaim 1, wherein a base station is configured to periodically transmit asingle-branch reference signal during each interval that is scheduledfor downlink communication.
 9. The method of claim 1, wherein: a) themessage includes or is preceded by a first single-branch referencesignal; and b) if the message occupies multiple symbol-times at a singlesubcarrier frequency, then the message further includes at least oneadditional single-branch reference signal embedded in the message. 10.The method of claim 1, further comprising: a) receiving a particularmessage element comprising a received I-branch amplitude and a receivedQ-branch amplitude, wherein one branch, of the received I and Qbranches, is transmitted with zero amplitude; b) calculating, accordingto a ratio of the received I-branch and Q-branch amplitudes, a receivedphase correction; c) calculating, according to a square root of a sum ofthe received I-branch amplitude squared plus the received Q-branchamplitude squared, a received sum-signal amplitude; and d) comparing thereceived sum-signal amplitude to the plurality of predeterminedamplitude levels.
 11. The method of claim 10, further comprising: a)after receiving the particular message element, receiving a subsequentmessage element comprising a subsequent I-branch amplitude and asubsequent Q-branch amplitude; b) calculating a sum-signal amplitudecomprising a square root of a sum of the subsequent I-branch amplitudesquared plus the subsequent Q-branch amplitude squared; c) calculating asum-signal phase of the subsequent message element comprising anarctangent of a ratio of the subsequent I-branch amplitude and thesubsequent Q-branch amplitude; d) calculating a corrected phasecomprising the sum-signal phase minus the received phase correction; ande) calculating a corrected I-branch amplitude comprising the sum-signalamplitude times a cosine of the corrected phase, and calculating acorrected Q-branch amplitude comprising the sum-signal amplitude times asine of the corrected phase.
 12. A wireless transmitter configured to:a) use a modulation scheme comprising: i) a first branch multiplexedwith an orthogonal second branch; and ii) a plurality of predeterminedamplitude levels; b) transmit a single-branch reference signalcomprising a reference first branch multiplexed with a reference secondbranch which is orthogonal to the reference first branch, wherein: c)the reference first branch is amplitude modulated according to one ofthe predetermined amplitude levels; and d) the reference second branchis amplitude modulated with zero amplitude.
 13. The wireless transmitterof claim 12, wherein: a) the plurality of predetermined amplitude levelscomprises a maximum predetermined amplitude level; and b) the referencefirst branch is amplitude modulated according to the maximumpredetermined amplitude level.
 14. The wireless transmitter of claim 12,wherein: a) the plurality of predetermined amplitude levels comprises amaximum predetermined amplitude level; and b) the first branch isamplitude modulated according to the maximum predetermined amplitudelevel times the square root of two.
 15. The wireless transmitter ofclaim 12, further configured to: a) transmit a message modulatedaccording to the modulation scheme, wherein: b) the message startsconcurrently with, or less than 3 symbol-times later than, thesingle-branch reference signal.
 16. The wireless transmitter of claim12, further configured to: a) transmit a message comprising messageelements, each message element comprising a first branch multiplexedwith an orthogonal second branch; b) wherein at least one messageelement is transmitted with the first branch modulated according to oneof the predetermined amplitude levels, and with the second branchmodulated at zero amplitude.
 17. Non-transitory computer-readable mediain a wireless receiver, the media containing instructions that whenimplemented in a computing environment cause a method to be performed,the method comprising: a) receiving a single-branch reference signalcomprising, in exactly one resource element, a reference I-branchamplitude multiplexed with an orthogonal reference Q-branch amplitude;b) measuring the reference I-branch amplitude and the reference Q-branchamplitude; c) calculating a reference sum-signal amplitude comprising asquare root of a sum of the reference I-branch amplitude squared plusthe reference Q-branch amplitude squared; d) calculating a referencesum-signal phase comprising an arctangent of a ratio of the referenceQ-branch amplitude divided by the reference I-branch amplitude; e)receiving a message comprising modulated message elements; f) for eachmessage element: i) measuring a received I-branch amplitude and areceived Q-branch amplitude; ii) calculating a received sum-signal phaseaccording to an arctangent of a ratio of the received Q-branch amplitudedivided by the received I-branch amplitude; and iii) calculating anadjusted sum-signal phase by subtracting the reference sum-signal phasefrom the received sum-signal phase.
 18. The media of claim 17, themethod further comprising, for each message element: a) calculating areceived sum-signal amplitude according to a square root of a sum of thereceived I-branch amplitude squared plus the received Q-branch amplitudesquared; b) calculating an adjusted I-branch amplitude comprising thereceived sum-signal amplitude times a cosine of the adjusted sum-signalphase; and c) calculating an adjusted Q-branch amplitude comprising thereceived sum-signal amplitude times a sine of the adjusted sum-signalphase.
 19. The media of claim 18, the method further comprising, foreach message element: a) comparing the adjusted I-branch amplitude to aplurality of predetermined amplitude levels, and selecting thepredetermined amplitude level closest to the adjusted I-branchamplitude; and b) comparing the adjusted Q-branch amplitude to theplurality of predetermined amplitude levels, and selecting thepredetermined amplitude level closest to the adjusted Q-branchamplitude.
 20. The media of claim 17, the method further comprising, foreach message element: a) calculating an amplitude correction ratiocomprising the reference sum-signal amplitude divided by a maximumamplitude level in a plurality of predetermined amplitude levels; and b)for each of the predetermined amplitude levels in the plurality,calculating a corrected amplitude level comprising the predeterminedamplitude level times the correction ratio.